Air spring with two part housing

ABSTRACT

Air spring which includes a flexible member which, on the one hand, is attached to a housing and, on the other hand, to a roll-off piston and which encloses an air volume; the surface of the housing, which faces toward the air volume of the air spring, is charged with the air pressure of the air volume; and, the air spring can be connected to the chassis of a motor vehicle with the interposition of an elastic bearing; the housing including at least two parts of which a first part serves the connection of the air spring to the chassis of a motor vehicle and a second part serves the attachment of the flexible member; and, the elastic bearing is configured to have an annular shape and is mounted between the two parts of the housing.

[0001] The invention relates to an air spring which has a flexiblemember which, on the one hand, is attached to a housing and, on theother hand, to a roll-off piston and encloses an air volume. The surfaceof the housing, which faces toward the air volume of the air spring, ischarged with the air pressure of the air volume and this surface of thehousing can be connected to the chassis of the motor vehicle at thehousing end with an elastic bearing disposed therebetween.

[0002] From the state of the art, air spring struts are known (see, forexample, EP 0 253 261 A1) which comprise a shock absorber and an airspring. The air spring is supported at the end of the roll-off piston onthe cylinder of the shock absorber. The piston of the shock absorber isinsertable into the cylinder and is connected to the housing via anelastic bearing for wobble movement and this permits a pivot movement ofthe shock absorber relative to the air spring. A further elastic bearingis mounted above the housing of the air spring via which the total airspring strut is connected to the chassis of a motor vehicle. Theadditional bearing makes possible a pivot movement of the entire airspring strut in its upper region. Because of the pivot movements,transverse forces and thrust stresses, which act on the flexible memberof the air spring with the deflections of the air spring, can be reducedand this leads to a longer service life of the flexible member. It is,however, noted that the total force flow of the wheel load passesthrough the elastic bearing mounted above the housing of the air spring.This must be configured correspondingly large and hard in order towithstand the loading generated by the wheel load. The bearing thereforerequires considerable space, which is dimensioned sparingly.Furthermore, the hard configuration of the bearing leads to limits oncomfort of the motor vehicle because the air spring of the spring strutas well as the elastic bearing, which is mounted above the housing ofthe air spring, exhibits a high spring stiffness when there are smallvibration amplitudes of the air spring strut. Vibrations having a smallvibration amplitudes are therefore poorly cushioned.

[0003] It is an object of the invention to provide an air spring whichis suitable for installation in an air spring strut and which air springhas an elastic bearing in the upper region for wobble movement whichbearing connects the air spring to the chassis of the motor vehicle andrequires little space.

[0004] According to the characteristic features of claim 1, the objectis solved in that: the housing of the air spring comprises at least twoparts of which a first part functions to connect the air spring to thechassis of a motor vehicle and a second part functions to attach theflexible member; and, that the elastic bearing is configured so as to beannular and is mounted between the two parts of the housing.

[0005] The elastic bearing connects the two parts of the housingair-tight to each other so that no air from the air volume of the airspring can escape to the outside between the two housing parts. Thesurface of the first part of the housing, which faces toward the airvolume of the air spring, is charged with the air pressure of the airvolume of the air spring. The surface of the first part of the housing,which is pressure-effective in the longitudinal direction of the airspring, corresponds in its size preferably approximately to thepressure-effective area of the air spring or is larger. In this way, itis ensured that the total wheel force is compensated by the force whichthe air pressure in the air volume of the air spring applies to thepressure-effective surface of the first part of the housing which isdirected in the longitudinal direction of the air spring. The staticwheel load does not operate on the elastic bearing.

[0006] The advantage achieved with the invention is especially that theforce flow of the wheel load leads directly from the air volume of theair spring to the chassis and, in this way, the elastic bearing of theair spring is no longer loaded completely by the wheel load. For thisreason, the elastic bearing can be configured to be small and requireslittle space. A further advantage of the invention is that the elasticbearing can be configured to be softer because of the lower loading bythe wheel load and, in this way, especially vibrations having a smallamplitude and a high vibration frequency can be cushioned by thebearing. Thus, the spring characteristic of the air spring is improvedfor the above-mentioned vibrations.

[0007] According to an embodiment of the invention of claim 2, the cleardiameter of the elastic bearing corresponds approximately to theeffective diameter of the air spring. The advantage of this furtherembodiment is that the elastic bearing is neither subjected tocompression nor tension by the air pressure in the air volume of the airspring and is subjected to only a minimum load. In this way, it ispossible to configure the elastic bearing to be especially small andespecially soft.

[0008] According to a first embodiment of the invention of claim 3, theroll-off piston of the air spring supports itself on a cylinder of ashock absorber whose piston is connected to the second part of thehousing and is insertable into the cylinder. Because of the elasticbearing between the first part and the second part of the housing of theair spring, it is ensured that the shock absorber is wobble movablerelative to the housing of the air spring in the upper region thereof.For this reason, an elastic bearing is not needed in the region of theattachment of the insertable piston at the second part of the housing.

[0009] According to a further embodiment of the invention of claim 4,the roll-off piston supports itself on a cylinder of a shock absorberwhose piston, which is insertable into the cylinder, is connecteddirectly to the chassis so as to be wobble-movable. The wobble-movableconnection of the piston to the chassis takes place preferably via anelastic bearing. The advantage of this embodiment is that the force flowof the dynamic forces is directed directly from the shock absorber tothe chassis of the motor vehicle. These dynamic forces operate on theshock absorber with a spring operation of the air spring strut. Theforce flow does not pass through the elastic bearing, which lies betweenthe two parts of the housing of the air spring, so that these dynamicforces do not have to be considered when designing the elastic bearing.In this way, the space needed to accommodate the elastic bearing can beminimized. Furthermore, the elastic bearing (via which the insertablepiston of the shock absorber is connected to the chassis of the motorvehicle) is optimally matched to the dynamic forces acting on the shockabsorber.

[0010] According to a further embodiment of the invention of claim 5,the elastic bearing has a form approximately of an annular section of aspherical surface and is mounted between two flange-like collars of thefirst and second parts of the housing. The pivot point of the spring inits upper region is then given by the center point of the sphericalsurface, which is completed starting from the annular-shaped bearing.The advantage of this embodiment is that the pivot point of the airspring can be precisely fixed in the upper region because of thesuggested configuration of the elastic bearing.

[0011] According to a further embodiment of the invention of claim 6,the elastic bearing is in the form of an annular cutout of a sphericalsurface and is mounted in such a manner between the two parts of thehousing, that the center point of the spherical surface, which iscompleted starting from the annular-shaped bearing, and therefore thepivot point of the air spring strut, lies in the region at which thepiston of the shock absorber is connected to the chassis. The advantageof this embodiment is that the spring strut can pivot about this pointfree of stresses.

[0012] According to an embodiment of the invention of claim 7, theelastic bearing comprises an elastomer component. The advantage of thisembodiment is that the elastic bearing in the form of an elastomercomponent can be configured especially simply. Furthermore, an elasticbearing in the form of an elastomer component is especially suitable toplace the two parts of the housing air-tight against each other.

[0013] A further embodiment of claim 8 is characterized in that: theflexible member projects beyond the second part at that end with whichit is attached to the second part of the housing; and, that the part ofthe flexible member, which projects beyond the second part, is attachedin such a manner to the first part, that a yielding part of the flexiblemember remains between the first and second part of the housing and theyielding part defines the elastic bearing.

[0014] The advantage of this embodiment is that for the elastic bearing,no separate component need be made available. A further advantage ofthis embodiment is that the flexible member can be attached to the partsof the housing simply with the aid of clamping rings and this attachmentensures an air-tight connection of the two parts of the housing.

[0015] The embodiments and additional advantages of the invention areexplained in connection with the following figures, wherein:

[0016]FIG. 1 shows an air spring strut;

[0017]FIG. 2 shows an air spring strut; and,

[0018]FIG. 3 shows an air spring strut.

[0019]FIG. 1 shows an air spring strut having a shock absorber 2 and anair spring 4. The roll-off piston 6 of the air spring supports itself onthe cylinder 8 of the shock absorber 2 so as to permit a wobblemovement. For this purpose, the cylinder 8 of the shock absorber 2 has aflange-like collar 10 and the roll-off piston 6 of the air spring 2 hasa flange-like collar 12. An elastic bearing 14 is mounted between thecollars (10, 12). At the upper end of the roll-off piston 6, theflexible member 16 of the air spring is attached which can roll off onthe roll-off piston 6 while forming a rolling lobe. The flexible member16 is attached to the housing 18 at the end lying opposite the roll-offpiston 6. The flexible member 6 encloses an air volume which is closedoff air-tight with respect to the atmosphere.

[0020] The housing 18 comprises two parts 18 a and 18 b of which thefirst part 18 a provides the connection of the air spring 4 andtherefore of the air spring strut to the chassis 22 of a motor vehicle.The connection can, for example, be provided by means of threadedfasteners (not shown). The second part 18 b of the housing 18 serves forthe attachment of the flexible member 16 of the air spring 4 and ispreferably configured, at the same time, as an outer guide for theflexible member 16 of the air spring 4 as shown in FIG. 1 and the otherfigures. The attachment of the flexible member 16 to the second part 18takes place, preferably, by means of a clamp ring 42. An annularlyconfigured elastic bearing in the form of an elastomer component 20 ismounted between the first part 18 a and the second part 18 b of thehousing 18. Preferably, the elastomer component 20 has approximately theform of an annular-shaped cutout of a spherical surface as also shown inFIG. 1. The elastomer component 20 lies with a precise fit between theflange-shaped sections 24 and 26 of the housing parts 18 a and 18 b sothat they lie air-tight one against the other.

[0021] The surface of the upper part 18 a of the housing 18 faces towardthe air volume of the air spring and is charged with the air pressure ofthe air volume of the air spring 4. The surface of the upper part 18 ais pressure-effective in the longitudinal direction of the air springstrut and corresponds, with respect to its size, preferablyapproximately to the pressure-effective area of the air spring 4 (thediameter of the pressure-effective surface of the air spring 2 isidentified in FIG. 1 with D_(w); the outer boundary line of thepressure-effective surface lies at the location at which the tangents onthe flexible member 16 of the air spring run perpendicularly to thespring force or supporting force). In this way, it is ensured that thetotal wheel load force (indicated by the arrow above the chassis 22) iscompensated by the force which the air pressure in the air volume of theair spring 4 applies to the pressure-effective area of the housing 18 aaligned in the longitudinal direction of the air spring strut. The wheelload then does not act on the elastomer component 20.

[0022] Furthermore, the clear diameter of the elastomer component 20corresponds approximately to the diameter of the pressure-effectivecross-sectional surface of the air spring 4 so that neither tensile norcompressive forces act on the elastomer component 20.

[0023] The housing part 18 b of the housing 18 includes a cover 28 onwhich the piston 30 is attached with a threaded fastener 32. The piston30 is insertable into the cylinder 8 of the shock absorber 2. The airspring 4 and the shock absorber 2 are journalled for wobble movementrelative to the chassis 22 by the elastomeric component 20. Openings 34are provided in the cover 28 of the housing part 18 b and these openingsmake possible a pressure compensation of the air pressure on both sidesof the cover 28. In this way, it is ensured that the surface of thehousing part 18 a, which is pressure-effective in the longitudinaldirection of the air spring strut, is always charged with the airpressure in the air spring 2 and, in this way, this surface can supportat least a part of the wheel load.

[0024]FIG. 2 shows an air spring strut which is substantially configuredas the air spring strut shown in FIG. 1. In the air spring strut, whichis shown in FIG. 2, the housing part 18 b, however, does not have acover 28 on which the piston 30 of the shock absorber 2 is attached.Rather, the piston 30 is guided directly to the chassis 22 of the motorvehicle and is there supported relative to the chassis for wobblemovement in the housing part 18 a with the aid of elastomer components36 and 38.

[0025] The annular elastic bearing is mounted between the two housingparts 18 a and 18 b and is in the form of an elastomeric component 20.In the embodiment shown in FIG. 2, this bearing also preferably has theform of an annular-shaped section of a spherical surface and liesbetween flange-like sections 24 and 26 of the housing parts 18 a and 18b. The elastomer component 20 is so aligned that the center point 40 ofa spherical surface lies in the region in which the piston 30 of theshock absorber 2 is connected to the chassis. The spherical surface iscompleted starting from the ring-shaped bearing. In this way, it isensured that the shock absorber 2 and the air spring 4 have wobblemovement about the same point relative to the chassis 22 in the upperchassis-close region.

[0026]FIG. 3 shows an air spring strut, which is configuredsubstantially as the air spring strut shown in FIG. 2. Here too, thepiston 30 is guided directly to the chassis 22 of the motor vehicle andis supported relative thereto with the aid of elastomeric components 36and 38 for wobble movement in the housing part 18 a.

[0027] The flexible member 16 is attached to the second part 18 b of thehousing 18 with the aid of the clamp ring 42 and at the end where theattachment lies, the flexible member projects beyond the second part 18b of the housing 18. The part of the flexible member 16, which projectsbeyond the housing part 18 b is attached with the aid of a clamp ring,44to the housing part 18 a. In the air spring strut, the housing parts 18a and 18 b as so spaced from each other that a yielding part of theflexible member 16 remains between these housing parts and forms theelastic bearing 20. Because of the inner pressure of the air spring 4,this part of the flexible member 16 is expanded radially outwardly sothat the form results, which is shown in FIG. 3. The air spring 4 isconnected for wobble movement to the housing part 18 a via the elasticbearing 20 (which is part of the flexible member 16) and is therewithconnected to the chassis 22 of the motor vehicle. Reference List  2shock absorber  4 air spring  6 roll-off piston  8 cylinder 10, 12flange-like collar 14 elastic bearing 16 flexible member 18 housing 18a,18b part of housing 18 20 elastomer component 22 chassis 24, 26flange-like sections 28 cover 30 piston 32 threaded fastener 34 openings36, 38 elastomer components 40 center point 42, 44 clamp ring

1. Air spring (4) which comprises: a flexible member (16) which, on theone hand, is attached to a housing (18) and, on the other hand, to aroll-off piston (6) and which encloses an air volume; the surface of thehousing (18), which faces toward the air volume of the air spring (4),is charged with the air pressure of the air volume; and, the air springcan be connected to the chassis (22) of a motor vehicle with theinterposition of an elastic bearing (20); characterized in that: thehousing (18) includes at least two parts (18 a, 18 b) of which a firstpart (18 a) serves the connection of the air spring (4) to the chassis(22) of a motor vehicle and a second part (18 b) serves the attachmentof the flexible member (16); and, that the elastic bearing (20) isconfigured to have an annular shape and is mounted between the two parts(18 a, 18 b) of the housing (18).
 2. Air spring (4) of claim 1,characterized in that the clear diameter of the elastic bearing (20)corresponds approximately to the effective diameter of the air spring(4).
 3. Air spring (4) of one of the claims 1 to 2, characterized inthat the roll-off piston (6) is supported on a cylinder (8) of a shockabsorber (2) and the piston (30) of the shock absorber is insertableinto the cylinder (8) and is connected to the second part (18 b) of thehousing (18).
 4. Air spring (4) of one of the claims 1 to 2,characterized in that the roll-off piston (6) is supported on a cylinder(8) of a shock absorber (2) and the piston (30) of the shock absorber isinsertable into the cylinder (8) and is connected directly to thechassis (22) for wobble movement.
 5. Air spring (4) of one of the claims1 to 4, characterized in that the elastic bearing (20) has approximatelythe form of an annular-shaped section of a spherical surface and ismounted between flange-like sections (24, 26) of the first and secondparts (18 a, 18 b) of the housing (18).
 6. Air spring (4) of one of theclaims 4 and 5, characterized in that the elastic bearing (20) ismounted in the form of an annular-shaped section between the two parts(18 a, 18 b) of the housing (18) in such a manner that the center pointof the spherical surface, which is completed starting from theannular-shaped section, lies in the region at which the piston (30) ofthe shock absorber (2) is connected to the chassis (22).
 7. Air spring(4) of one of the claims 1 to 6, characterized in that the elasticbearing (20) comprises an elastomeric component.
 8. Air spring (4) ofone of the claims 1 to 4, characterized in that: the flexible member(16) projects beyond the second part (18 b) at the end with which it isattached to the second part (18 b) of the housing (18); and, that thepart of the flexible member (16), which projects beyond the second part(18 b), is attached to the first part (18 a) of the housing (18) in sucha manner that a yielding part of the flexible member (16) remainsbetween the first part (18 a) and the second part (18 b) of the housingand this yielding part defines the elastic bearing (20).